Day–night variation and size distribution of water-soluble inorganic ions in particulate matter in Ulsan, South Korea

In the present study, 11 size classes of particulate matter were collected from a semi-rural site in industrial city Ulsan, South Korea 2019 to investigate distribution and day–night variation water-soluble inorganic ions (WSIIs). Approximately 70% detected WSIIs found fine particles, with Na+, Ca2+, Cl?, NO3? dominant (~70%) coarse particles SO42?, NO3?, NH4+ (SNA) particles. Monthly total was observed, highest average concentration April for both (2.71 ?g/m3) (5.75 ?g/m3). Given that this month is characterized by prevailing southeasterly winds, these high levels may represent adverse effects activity. Coefficients divergence individual exhibited large variability, which indicative significant differences meteorology, chemistry, source contributions. The distributions K+, F?, SO42? bimodal, while Mg2+, unimodal. Peaks generally at 1.8–5.6 ?m 0.18–0.56 respectively. By plotting linear relationship between mole charge ratios SNA, we mainly result heterogeneous reactions HNO3 sea salts or crustal species, homogeneous reaction NH3 played crucial role formation conclusion, though apparent, especially pathways similar day night. Based on verification mechanisms site, influence activity secondary PM urban areas can be investigated further.